Long range non-contact sensors such as RGB cameras, depth cameras, and laser scanners are widely used, for example in robotics for object recognition and pose estimation. One application for these relatively long range sensors is to obtain data for robotic grasp planning prior to manipulation. Contact sensors such as tactile pressure sensors are commonly used during the process of manipulation to provide force feedback information to a grasp controller.
The acoustic proximity sensor disclosed herein is a type of “pretouch” sensor. Pretouch sensors are non-contact sensors suitable for use to detect close proximity to an object, e.g., at a range that is shorter than optical devices but longer than contact-based tactile sensing. A novel pretouch or proximity sensor, sometimes called a “seashell effect pretouch sensor” has been found to work for close range proximity sensing on a wide variety of materials. For example, the seashell effect pretouch sensor may be used for both grasp control and grasp planning in robotic systems. They may also be used in a non-optical, non-contact system for obtaining three dimensional data for an object.
Pretouch sensing is beneficial for robotic manipulation because it provides reliable geometric information in the last centimeter before contact. A disadvantage of tactile sensing for collecting local geometric information is that contacting the object may displace and/or deform the object. Pretouch sensing may be implemented in a manner that is not subject to problems associated with the manipulator device occluding the camera. The pretouch sensor may be integrated directly into the end effector of a robotic manipulator. Similarly, there are typically no camera-to-hand registration errors because the sensor is in the coordinate frame of the hand. A further distinction between pretouch sensing and depth sensing technologies is that the latter typically fail below some minimum distance.
Compared to tactile sensing, one can think, of a pretouch sensor as a sensor that detects surface proximity, but has no lower limit on detectable force, and thus is able to sense arbitrarily compliant objects.
A pretouch sensor that relies on electric field sensing is disclosed in U.S. Patent Application Publication No. US 2010/0256814, which is hereby incorporated by reference in its entirety. Electric field pretouch sensing has many desirable properties, but typically rely on the properties of materials that are conductive or have high dielectric constant. Optical pretouch depends on surface albedo, and thus fails in some of the same cases as the long range vision sensors: transparent or specular objects. Thus optical pretouch sensors may fail to complement the longer range 3D visual sensors used to plan grasps because they both rely on similar physical phenomena. Optical pretouch sensors and 3D visual sensors are therefore likely to fail in a correlated fashion. Seashell effect pretouch sensors such as those disclosed herein have the desirable characteristics of pretouch sensing systems using other technologies, but do not depend on electrical or optical material properties. Thus seashell effect (acoustic) pretouch sensors work on materials that are difficult for electric field pretouch, optical pretouch, and conventional vision/depth sensors.